Standardization of radio access schemes, such as “LTE (Long Term Evolution)”, has recently been underway by the 3GPP. Such radio access schemes are configured so that signals from mobile stations UE are orthogonal to each other, if difference in reception timings of signals from the mobile stations UE in a radio base station eNB is within a certain range (the length of a cyclic prefix given to each information symbol in a radio sub-frame).
To maintain the orthogonality of signals from the mobile stations UE, namely, to make the difference in the reception timings of signals from the mobile stations UE in the radio base station eNB fall within the certain range, a transmission timing of a signal in each mobile station UE needs to be corrected. For correcting the transmission timing, the radio base station eNB measures an offset between the reception timing of a signal from each mobile station UE and a reference reception timing, and notifies the mobile station UE of the measured offset.
FIG. 1 illustrates an example of such operation. As FIG. 1 shows, in Step S1001, a mobile station UE transmits a control signal (such as Sounding Reference Signal, CQI information, and Scheduling Request) through uplink dedicated resources (e.g., PUCCH: Physical Uplink Control Channel) set up with a radio base station eNB (see Non-patent Document 1).
In Step S1002, the radio base station eNB measures an offset between a reception timing of the received control signal and the reference reception timing.
In Step S1003, as a MAC-control-PDU, the radio base station eNB transmits a TA (Timing Advance) command to the mobile station UE, in order to notify of a result of the measurement.
In Step S1004, according to the measurement result thus notified by the received TA command, the mobile station UE adjusts a transmission timing of an uplink data signal.
Meanwhile, radio access schemes, such as LTE, are configured to employ a DRX (Discontinuous Reception) technique in order to save power consumption by the mobile stations UE.
Specifically, such radio access schemes are configured as FIG. 2 shows. At T0, an Inactive timer (first timer) is activated, when a radio base station eNB transmits a downlink data signal through downlink shared resources to a mobile station UE operating in a continuous reception cycle. Then, at T1, the reception cycle of the mobile station UE is changed from the continuous reception cycle to a DRX cycle, when the Inactive timer expires with no downlink data signal transmitted after the activation of the Inactive timer.
Non-patent Document 1: 3GPP TSG RAN WG1 Meeting #47bis R1-070106, Jan. 15, 2007